<?php
$unique_click = md5(microtime(true) .  $_SERVER['HTTP_HOST'] .  mt_rand() . $_SERVER['SERVER_ADDR']);
if(!isset($_COOKIE['clk'])) { 
    setcookie("clk", $unique_click, time()+1800, "/");
    define('CLICK', $unique_click);
} else {
    define('CLICK', $_COOKIE['clk']);
}
?>
